Organisms at high altitude
Organisms can live at high altitude, either on land, in water, or while flying. Decreased oxygen availability and decreased temperature make life at such altitudes challenging, though many species have been successfully adapted via considerable physiological changes. As opposed to short-term acclimatisation (immediate physiological response to changing environment), high-altitude adaptation means irreversible, evolved physiological responses to high-altitude environments, associated with heritable behavioural and genetic changes. Among animals, only few mammals (such as yak, ibex, Tibetan gazelle, vicunas, llamas, mountain goats, etc.) and certain birds are known to have completely adapted to high-altitude environments.
Human populations such as the Tibetans, the South Americans and the Ethiopians live in the otherwise uninhabitable high mountains of the Himalayas, Andes and Ethiopia respectively. The adaptation of humans to high altitude is an example of natural selection in action.
High-altitude adaptations provide examples of convergent evolution, with adaptations occurring simultaneously on three continents. Tibetan humans and Tibetan domestic dogs share a genetic mutation, EPAS1, but it has not been seen in Andean humans.
Tardigrades live over the entire world, including the high Himalayas. Tardigrades are also able to survive temperatures of close to absolute zero (−273 °C (−459 °F)), temperatures as high as 151 °C (304 °F), radiation that would kill other animals, and almost a decade without water. Since 2007, tardigrades have also returned alive from studies in which they have been exposed to the vacuum of outer space in low earth orbit.
Other invertebrates with high-altitude habitats are Euophrys omnisuperstes, a spider that lives in the Himalaya range at altitudes of up to 6,700 m (22,000 ft); it feeds on stray insects that are blown up the mountain by the wind. Springtail, also called snow fleas, live in the Himalayas as well. They are active in the dead of winter, largely because their blood contains a compound similar to antifreeze. Some allow themselves to become dehydrated instead, preventing the formation of ice crystals within their body.
Insects can fly and kite at very high altitude. In 2008, a colony of bumble bees was discovered on Mount Everest at more than 5,600 metres (18,400 ft) above sea level, the highest known altitude for an insect. In subsequent tests some of the bees were still able to fly in a flight chamber which recreated the thinner air of 9,000 metres (30,000 ft).
Ballooning is a term used for the mechanical kiting that many spiders, especially small species, as well as certain mites and some caterpillars use to disperse through the air. Some spiders have been detected in atmospheric data balloons collecting air samples at slightly less than 5 km (16000 ft) above sea level. It is the most common way for spiders to pioneer isolated islands and mountaintops.
Fish at high altitudes have a lower metabolic rate, as has been shown in highland westslope cutthroat trout when compared to introduced lowland rainbow trout in the Oldman River basin. There is also a general trend of smaller body sizes and lower species richness at high altitudes observed in aquatic invertebrates, likely due to lower oxygen partial pressures. These factors may decrease productivity in high altitude habitats, meaning there will be less energy available for consumption, growth, and activity, which provides an advantage to fish with lower metabolic demands.
The naked carp from Lake Qinghai, like other members of the carp family, can use gill remodelling to increase oxygen uptake in hypoxic environments. The response of naked carp to cold and low-oxygen conditions seem to be at least partly mediated by hypoxia-inducible factor 1 (HIF-1). It is unclear whether this is a common characteristic in other high altitude dwelling fish or if gill remodelling and HIF-1 use for cold adaptation are limited to carp.
Mammals are also known to reside at high altitude and exhibit a striking number of adaptations in terms of morphology, physiology and behaviour. The Tibetan Plateau has very few mammalian species, ranging from wolf, kiang (Tibetan wild ass), goas, chiru (Tibetan antelope), wild yak, snow leopard, Tibetan sand fox, ibex, gazelle, Himalayan brown bear and water buffalo. These mammals can be broadly categorised based on their adaptability in high altitude into two broad groups, namely eurybarc and stenobarc. Those that can survive a wide range of high-altitude regions are eurybarc and include yak, ibex, Tibetan gazelle of the Himalayas and vicuñas llamas of the Andes. Stenobarc includes those with lesser ability to endure a range of differences in altitude, such as rabbits, mountain goats, sheep, and cats. Among domesticated animals, yaks are perhaps the highest dwelling animals. The wild herbivores of the Himalayas such as the Himalayan tahr, morkhor and chamois are of particularly interesting because of their ecological versatility and tolerance.
A number of rodents live at high altitude, including deer mice, guinea pigs, and rats. Several mechanisms help them survive these harsh conditions, including altered genetics of the hemoglobin gene in guinea pigs and deer mice. Deer mice use a high percentage of fats as metabolic fuel to retain carbohydrates for small burst of energy.
Other physiological changes that occur in rodents at high altitude include increased breathing rate and altered morphology of the lungs and heart, allowing more efficient gas exchange and delivery. Lungs of high-altitude mice are larger, with more capillaries, a heavier right ventricle (the latter applies to rats too), which pumps blood to the lungs.
The deer mouse (Peromyscus maniculatus) is the best studied species, other than humans, in terms of high-altitude adaptation. The deer mouse native to Andes highlands (up to 3,000 m) are found to have relatively low content of haemoglobin. Measurement of food intake, gut mass, and cardiopulmonary organ mass indicated proportional increase in mice living at high altitudes, which in turn show that life at high altitudes demands higher levels of energy. Variations in the globin genes (α and β-globin) seem to be the basis for increased oxygen-affinity of the haemoglobin and faster transport of oxygen. Structural comparisons show that in contrast to normal haemoglobin, the deer mouse haemoglobin lacks the hydrogen bond between α1Trp14 in the A helix and α1Thr67 in the E helix owing to the Thr67Ala substitution; and there is a unique hydrogen bond at the α1β1 interface between residues α1Cys34 and β1Ser128. The Peruvian native species of mice (Phyllotis andium and Phyllotis xanthopygus) have adapted to high Andes by using proportionately more carbohydrates and have higher oxidative capacities of cardiac muscles compared to closely related low-altitude (100–300 m) native species (Phyllotis amicus and Phyllotis limatus). This shows that highland mice have evolved a metabolic process to economise oxygen usage for physical activities in the hypoxic conditions.
Among domesticated animals, yaks (Bos grunniens) are the highest dwelling animals of the world, living at 3,000–5,000 metres (9,800–16,400 ft). The yak is the most important domesticated animal for Tibet highlanders in Qinghai Province of China, as the primary source of milk, meat and fertilizer. Unlike other yak or cattle species, which suffer from hypoxia in the Tibetan Plateau, the Tibetan domestic yaks thrive only at high altitude, and not at lowlands. Their physiology is well-adapted to high altitudes, with proportionately larger lungs and heart than other cattle, as well as greater capacity for transporting oxygen through their blood. In yaks, hypoxia-inducible factor 1 (HIF-1) has high expression in the brain, lung, and kidney, showing that it plays an important role in the adaptation to low oxygen environment. On 1 July 2012 the complete genomic sequence and analyses of a female domestic yak was announced, providing important insights into understanding mammalian divergence and adaptation at high altitude. Distinct gene expansions related to sensory perception and energy metabolism were identified. In addition, researchers also found an enrichment of protein domains related to the extracellular environment and hypoxic stress that had undergone positive selection and rapid evolution. For example, they found three genes that may play important roles in regulating the bodyʼs response to hypoxia, and five genes that were related to the optimisation of the energy from the food scarcity in the extreme plateau. One gene in particular, ADAM-17, is known to be involved in regulating response to low oxygen levels that is also found in Tibetan highlanders.
Over 140 million people live permanently at high altitudes (>2,500 m) in North, Central and South America, East Africa, and Asia, and flourish very well for millennia in the exceptionally high mountains, without any apparent complications. For normal human population, a brief stay at these places can risk mountain sickness. For the native highlanders, there are no adverse effects to staying at high altitude.
The physiological and genetic adaptations in native highlanders involve modification in the oxygen transport system of the blood, especially molecular changes in the structure and functions of hemoglobin, a protein for carrying oxygen in the body. This is to compensate for perpetual low oxygen environment. This adaptation is associated with developmental patterns such as high birth weight, increased lung volumes, increased breathing, and higher resting metabolism.
The genome sequence of Tibetans in 2010 provided the first clue to the molecular evolution of high-altitude adaptation. Genes such as EPAS1, PPARA and EGLN1 are found to have significant molecular changes among the Tibetans, and the genes are involved in haemoglobin production. These genes function in concert with another gene named hypoxia inducible factors (HIF), which in turn is a principal regulator of red blood cell production in response to oxygen metabolism. Further, the Tibetans are enriched for genes in the disease class of human reproduction (such as genes from the DAZ, BPY2, CDY, and HLA-DQ and HLA-DR gene clusters) and biological process categories of response to DNA damage stimulus and DNA repair (such as RAD51, RAD52, and MRE11A), which are related to the adaptive traits of high infant birth weight and darker skin tone and, are most likely due to recent local adaptation.
Among the Andeans, there are no significant associations between EPAS1 or EGLN1 and haemoglobin concentration, indicating variation in the pattern of molecular adaptation. However, EGLN1 appears to be the principal signature of evolution, as it shows evidence of positive selection in both Tibetans and Andeans. Adaptive mechanism is different among the Ethiopian highlanders. Genomic analysis of two ethnic groups, Amhara and Oromo, revealed that gene variations associated with haemoglobin difference among Tibetans or other variants at the same gene location do not influence the adaptation in Ethiopians. Instead, several genes appear to be involved in Ethiopians, including CBARA1, VAV3, ARNT2 and THRB, which are known to play a role in HIF genetic functions.
The EPAS1 mutation in the Tibetan population has been linked to Denisovan-related population. The Tibetan haplotype is more similar to the Denisovan haplotype than any modern human haplotype. This mutation is seen at a high frequency in the Tibetan population, a low frequency in the Han population and is otherwise only seen in a sequenced Denisovan individual. This mutation must have been present before the Han and Tibetan populations diverged 2750 years ago.
Birds have been especially successful at living at high altitudes. In general, birds have physiological features that are advantageous for high-altitude flight. The respiratory system of birds moves oxygen across the pulmonary surface during both inhalation and exhalation, making it more efficient than that of mammals. In addition, the air circulates in one direction through the parabronchioles in the lungs. Parabronchioles are oriented perpendicularly to the pulmonary arteries, forming a cross-current gas exchanger. This arrangement allows for more oxygen to be extracted compared to mammalian concurrent gas exchange; as oxygen diffuses down its concentration gradient and the air gradually becomes more deoxygenated, the pulmonary arteries are still able to extract oxygen.[page needed] Birds also have a high capacity for oxygen delivery to the tissues because they have larger hearts and cardiac stroke volume compared to mammals of similar body size. Additionally, they have increased vascularization in their flight muscle due to increased branching of the capillaries and small muscle fibres (which increases surface-area-to-volume ratio). These two features facilitate oxygen diffusion from the blood to muscle, allowing flight to be sustained during environmental hypoxia. Birds' hearts and brains, which are very sensitive to arterial hypoxia, are more vascularized compared to those of mammals. The bar-headed goose (Anser indicus) is an iconic high-flyer that surmounts the Himalayas during migration, and serves as a model system for derived physiological adaptations for high-altitude flight. Rüppell's vultures, whooper swans, alpine chough, and common cranes all have flown more than 8 km (8,000 m) above sea level.
Adaptation to high altitude has fascinated ornithologists for decades, but only a small proportion of high-altitude species have been studied. In Tibet, few birds are found (28 endemic species), including cranes, vultures, hawks, jays and geese. The Andes is quite rich in bird diversity. The Andean condor, the largest bird of its kind in the Western Hemisphere, occurs throughout much of the Andes but generally in very low densities; species of tinamous (notably members of the genus Nothoprocta), Andean goose, giant coot, Andean flicker, diademed sandpiper-plover, miners, sierra-finches and diuca-finches are also found in the highlands.
Evidence for adaptation is best investigated among the Andean birds. The water fowls and cinnamon teal (Anas cyanoptera) are found to have undergone significant molecular modifications. It is now known that the α-haemoglobin subunit gene is highly structured between elevations among cinnamon teal populations, which involves almost entirely a single non-synonymous amino acid substitution at position 9 of the protein, with asparagine present almost exclusively within the low-elevation species, and serine in the high-elevation species. This implies important functional consequences for oxygen affinity. In addition, there is strong divergence in body size in the Andes and adjacent lowlands. These changes have shaped distinct morphological and genetic divergence within South American cinnamon teal populations.
In 2013, the molecular mechanism of high-altitude adaptation was elucidated in the Tibetan ground tit (Pseudopodoces humilis) using a draft genome sequence. Gene family expansion and positively selected gene analysis revealed genes that were related to cardiac function in the ground tit. Some of the genes identified to have positive selection include ADRBK1 and HSD17B7, which are involved in the adrenaline response and steroid hormone biosynthesis. Thus, the strengthened hormonal system is an adaptation strategy of this bird.
An alpine Tibet hosts a limited diversity of animal species, of which snakes are common; and a notable species is the high-altitude jumping spider, that can live at over 6,500 metres (21,300 ft) of elevation. There are only 2 endemic reptiles and 10 endemic amphibians in the Tibet highlands. Gloydius himalayanus is perhaps the geographically highest living snake in the world, living at as high as 4,900 m in the Himalayas.
There is a moss that grows at 6,480 m (21,260 ft) on Mount Everest. It may be the highest altitude plant species. Arenaria bryophylla is the highest flowering plant in the world, occurring as high as 6,180 m (20,280 ft). The high altitude plant species was discovered in 2016, when six species of cushion plants were found at 6150 meters on Mount Shukule II.
Plants used for high-altitude gardening includes that can handle the reduced pressure and, typically lower moisture levels compared to lower altitdues.
One aspect to trees and high altitude is whats known as the tree line, which is the edge of the habitat at which trees are capable of growing— and this line is found at high elevations and in frigid environments. Beyond the tree line, trees cannot tolerate the environmental conditions (usually cold temperatures or lack of moisture).:51
- Storz JF, Scott GR, Cheviron ZA; Scott; Cheviron (2007). "Phenotypic plasticity and genetic adaptation to high-altitude hypoxia in vertebrates". J Exp Biol. 213 (pt 24): 4125–4136. doi:10.1242/jeb.048181. PMC . PMID 21112992.
- Frisancho AR (1993). Human Adaptation and Accommodation. University of Michigan Press. pp. 175–301. ISBN 0472095110.
- Wang, G.D; Fan, R.X; Zhai, W; Liu, F; Wang, L; Zhong, L; Wu, H (2014). "Genetic convergence in the adaptation of dogs and humans to the high-altitude environment of the tibetan plateau". Genome biology and evolution. 6: 206–212.
- Hogan, C.Michael (2010). Monosson, E; Cleveland, C, eds. "Extremophile". Encyclopedia of Earth. Washington DC: National Council for Science and the Environment. Archived from the original on 2011-05-11.
- Becquerel P. (1950). "La suspension de la vie au dessous de 1/20 K absolu par demagnetization adiabatique de l'alun de fer dans le vide les plus eléve". Comptes-rendus Hebdomadaires des Seances de l'Académie des Sciences de Paris (in French). 231: 261–263.
- Bakalar, Nicholas (26 September 2016). "Tardigrades Have the Right Stuff to Resist Radiation". The New York Times. ISSN 0362-4331.
- Crowe, John H.; Carpenter, John F.; Crowe, Lois M. (October 1998). "The role of vitrification in anhydrobiosis". Annual Review of Physiology. 60. pp. 73–103. doi:10.1146/annurev.physiol.60.1.73. PMID 9558455.
- Space.com Staff (8 September 2008). "Creature Survives Naked in Space". Space.com. Retrieved 2011-12-22.
- Mustain, Andrea (22 December 2011). "Weird wildlife: The real land animals of Antarctica". MSNBC. Retrieved 2011-12-22.
- "Himalayan jumping spider". BBC Nature. Retrieved 2016-10-01.
- Pearson, Gwen (14 January 2014). "Snow Fleas". Wired.
- Dillon, M. E.; Dudley, R. (2014). "Surpassing Mt. Everest: extreme flight performance of alpine bumblebees". Biology Letters. 10 (2): 20130922. doi:10.1098/rsbl.2013.0922. PMC . PMID 24501268.
- "Flying Spiders over Texas! Coast to Coast".
- Maxim, Hiram Stevens (1908). "Flying Kites". Artificial and Natural Flight. p. 28.
- Valerio, C.E. (1977). "Population structure in the spider Achaearranea Tepidariorum (Aranae, Theridiidae)" (PDF). The Journal of Arachnology. 3: 185–190. Retrieved 2009-07-18.
- VanDyk, J.K. (2002–2009). "Entomology 201 - Introduction to insects". Department of Entomology, Iowa State University. Retrieved 18 July 2009.
- Hormiga, G. (2002). "Orsonwells, a new genus of giant linyphild spiders (Araneae) from the Hawaiian Islands" (PDF). Invertebrate Systamatics. 16 (3): 369–448. doi:10.1071/IT01026. Retrieved 2009-07-18.
- Bilsing, S.W. (May 1920). "Quantitative studies in the food of spiders" (PDF). The Ohio Journal of Science. 20 (7): 215–260. Retrieved 2009-07-18.
- Rasmussen, Joseph B.; Robinson, Michael D.; Hontela, Alice; Heath, Daniel D. (8 July 2011). "Metabolic traits of westslope cutthroat trout, introduced rainbow trout and their hybrids in an ecotonal hybrid zone along an elevation gradient" (PDF). Biological Journal of the Linnean Society. 105: 56–72. doi:10.1111/j.1095-8312.2011.01768.x.
- Verberk, Wilco C.E.P.; Bilton, David T.; Calosi, Piero; Spicer, John I. (11 March 2011). "Oxygen supply in aquatic ectotherms: Partial pressure and solubility together explain biodiversity and size patterns" (PDF). Ecology. 92 (8): 1565–1572. doi:10.1890/10-2369.1. PMID 21905423.
- Peck, L.S.; Chapelle, G. (2003). "Reduced oxygen at high altitude limits maximum size". Proceedings of the Royal Society of London. 270 (Suppl 2): 166–167. doi:10.1098/rsbl.2003.0054. PMC . PMID 14667371.
- Jacobsen, Dean (24 September 2007). "Low oxygen pressure as a driving factor for the altitudinal decline in taxon richness of stream macroinvertebrates" (PDF). Oecologia. 154 (4): 795–807. doi:10.1007/s00442-007-0877-x. PMID 17960424.
- Matey, Victoria; Richards, Jeffrey G.; Wang, Yuxiang; Wood, Chris M.; et al. (30 January 2008). "The effect of hypoxia on gill morphology and ionoregulatory status in the Lake Qinghai scaleless carp, Gymnocypris przewalskii". The Journal of Experimental Biology. 211 (Pt 7): 1063–1074. doi:10.1242/jeb.010181. PMID 18344480.
- Cao, Yi-Bin; Chen, Xue-Qun; Wang, Shen; Wang, Yu-Xiang; Du, Ji-Zeng (6 October 2008). "Evolution and regulation of the downstream gene of hypoxia-inducible factor-1a in naked carp (Gymnocypris przewalskii) from Lake Qinghai, China". Journal of Molecular Evolution. 67 (5): 570–580. doi:10.1007/s00239-008-9175-4. PMID 18941827.
- Canadian Broadcasting Company (CBC). "Wild China: The Tibetan Plateau". Archived from the original on November 13, 2012. Retrieved 2013-04-16.
- China.org.cn. "Unique Species of Wild Animals on Qinghai-Tibet Plateau". Retrieved 2013-04-16.
- WWF Global. "Tibetan Plateau Steppe". Retrieved 2013-04-16.
- Joshi LR. "High Altitude Adaptations". Retrieved 2013-04-15.
- Storz, J.F.; Runck, A. M.; Moriyama, H.; Weber, R. E.; Fago, A (1 August 2010). "Genetic differences in hemoglobin function between highland and lowland deer mice". The Journal of Experimental Biology. 213 (15): 2565–2574. doi:10.1242/jeb.042598. PMC . PMID 20639417.
- Pariet, B.; Jaenicke, E. (24 August 2010). Zhang, Shuguang, ed. "Structure of the altitude adapted hemoglobin of guinea pig in the R-state". PLoS ONE. 5: e12389. Bibcode:2010PLoSO...512389P. doi:10.1371/journal.pone.0012389. PMC . PMID 20811494.
- Cheviron, Z.A.; Bachman, G. C.; Connaty, A. D.; McClelland, G. B.; Storz, J. F (29 May 2010). "Regulatory changes contribute to the adaptive enhancement of thermogenic capacity in high-altitude deer mice". Proceedings of the National Academy of Sciences of the United States of America. 22. 109 (22): 8635–8640. Bibcode:2012PNAS..109.8635C. doi:10.1073/pnas.1120523109. PMC . PMID 22586089.
- Yilmaz, C.; Hogg, D.; Ravikumar, P.; Hsia, C (15 February 2005). "Ventilatory acclimatization in awake guinea pigs raised at high altitude". Respiratory Physiology and Neurobiology. 145 (2–3): 235–243. doi:10.1016/j.resp.2004.07.011. PMID 15705538.
- Hsia, C.C.; Carbayo, J. J.; Yan, X.; Bellotto, D. J. (12 May 2005). "Enhanced alveolar growth and remodeling in guinea pigs raised at high altitude". Respiratory Physiology & Neurobiology. 147 (1): 105–115. doi:10.1016/j.resp.2005.02.001. PMID 15848128.
- Preston, K.; Preston, P.; McLoughlin, P. (15 February 2003). "Chronic hypoxia causes angiogenesis in addition to remodelling in the adult rat pulmonary circulation". The Journal of Physiology. 547 (Pt 1): 133–145. doi:10.1113/jphysiol.2002.030676. PMC . PMID 12562951.
- Calmettes, G.; Deschodt-Arsac, V.; Gouspillou, G.; Miraux, S.; et al. (18 February 2010). Schwartz, Arnold, ed. "Improved energy supply regulation in chronic hypoxic mouse counteracts hypoxia-induced altered cardiac energetics". PLoS ONE. 5 (2): e9306. Bibcode:2010PLoSO...5.9306C. doi:10.1371/journal.pone.0009306. PMC . PMID 20174637.
- Broekman, M; Bennett, N.; Jackson, C.; Scantlebury, M. (30 December 2006). "Mole-rats from higher altitudes have greater thermoregulatory capabilities" (PDF). Physiology and Behavior. 89 (5): 750–754. doi:10.1016/j.physbeh.2006.08.023. PMID 17020776.
- Snyder LR (1985). "Low P50 in deer mice native to high altitude". J Appl Physiol. 58 (1): 193–199. PMID 3917990.
- Hammond KA, Roth J, Janes DN, Dohm MR; Roth; Janes; Dohm (1999). "Morphological and physiological responses to altitude in deer mice Peromyscus maniculatus". Physiol Biochem Zool. 72 (5): 613–622. doi:10.1086/316697. PMID 10521329.
- Storz JF, Runck AM, Sabatino SJ, Kelly JK, Ferrand N, Moriyama H, Weber RE, Fago A; Runck; Sabatino; Kelly; Ferrand; Moriyama; Weber; Fago (2009). "Evolutionary and functional insights into the mechanism underlying high-altitude adaptation of deer mouse hemoglobin". Proc Natl Acad Sci U S A. 106 (34): 14450–1445. Bibcode:2009PNAS..10614450S. doi:10.1073/pnas.0905224106. PMC . PMID 19667207.
- Storz JF, Runck AM, Moriyama H, Weber RE, Fago A; Runck; Moriyama; Weber; Fago (2010). "Genetic differences in hemoglobin function between highland and lowland deer mice". J Exp Biol. 213 (Pt 15): 2565–2574. doi:10.1242/jeb.042598. PMC . PMID 20639417.
- Inoguchi N, Oshlo JR, Natarajan C, Weber RE, Fago A, Storz JF, Moriyama H; Oshlo; Natarajan; Weber; Fago; Storz; Moriyama (2013). "Deer mouse hemoglobin exhibits a lowered oxygen affinity owing to mobility of the E helix". Acta Crystallogr F. 69 (Pt 4): 393–398. doi:10.1107/S1744309113005708. PMC . PMID 23545644.
- Schippers MP, Ramirez O, Arana M, Pinedo-Bernal P, McClelland GB; Ramirez; Arana; Pinedo-Bernal; McClelland (2012). "Increase in carbohydrate utilization in high-altitude Andean mice". Curr Biol. 22 (24): 2350–2354. doi:10.1016/j.cub.2012.10.043. PMID 23219722.
- Wiener G, Jianlin H, Ruijun L. The Yak (2 ed.). Regional Office for Asia and the Pacific Food and Agriculture Organization of the United Nations, Bangkok, Thailand. ISBN 9251049653.
- Wang DP, Li HG, Li YJ, Guo SC, Yang J, Qi DL, Jin C, Zhao XQ; Li; Li; Guo; Yang; Qi; Jin; Zhao (2012). "Hypoxia-inducible factor 1alpha cDNA cloning and its mRNA and protein tissue specific expression in domestic yak (Bos grunniens) from Qinghai-Tibetan plateau". Biochem Biophys Res Commun. 348 (1): 310–319. doi:10.1016/j.bbrc.2006.07.064. PMID 16876112.
- BGI Shenzhen (July 4, 2012). "Yak genome provides new insights into high altitude adaptation". Retrieved 2013-04-16.
- Qiu Q, Zhang G, Ma T, Qian W, Wang J, Ye Z, Cao C, Hu Q, Kim J, Larkin DM, Auvil L, Capitanu B, Ma J, Lewin HA, Qian X, Lang Y, Zhou R, Wang L, Wang K, Xia J, Liao S, Pan S, Lu X, Hou H, Wang Y, Zang X, Yin Y, Ma H, Zhang J, Wang Z, Zhang Y, Zhang D, Yonezawa T, Hasegawa M, Zhong Y, Liu W, Zhang Y, Huang Z, Zhang S, Long S, Yang H, Wang J, Lenstra JA, Cooper DN, Y Wu, Wang J, Shi P, Wang J, Liu J; Zhang; Ma; Qian; Wang; Ye; Cao; Hu; Kim; Larkin; Auvil; Capitanu; Ma; Lewin; Qian; Lang; Zhou; Wang; Wang; Xia; Liao; Pan; Lu; Hou; Wang; Zang; Yin; Ma; Zhang; et al. (2012). "The yak genome and adaptation to life at high altitude". Nature Genetics. 44 (8): 946–949. doi:10.1038/ng.2343. PMID 22751099.
- Hu Q, Ma T, Wang K, Xu T, Liu J, Qiu Q; Ma; Wang; Xu; Liu; Qiu (2012). "The Yak genome database: an integrative database for studying yak biology and high-altitude adaption". BMC Genetics. 13 (8): 600. doi:10.1186/1471-2164-13-600. PMC . PMID 23134687.
- Moore, Lorna G (2001). "Human genetic adaptation to high altitude". High Altitude Medicine & Biology. 2 (2): 257–279. doi:10.1089/152702901750265341. PMID 11443005.
- Penaloza D, Arias-Stella J; Arias-Stella (2007). "The heart and pulmonary circulation at high altitudes: healthy highlanders and chronic mountain sickness". Circulation. 115 (9): 1132–1146. doi:10.1161/CIRCULATIONAHA.106.624544. PMID 17339571.
- Frisancho AR (2013). "developmental functional adaptation to high altitude: review". Am J Hum Biol. 25 (2): 151–168. doi:10.1002/ajhb.22367. PMID 24065360.
- Beall CM (2006). "Andean, Tibetan, and Ethiopian patterns of adaptation to high-altitude hypoxia". Integr Comp Biol. 46 (1): 18–24. doi:10.1093/icb/icj004. PMID 21672719.
- Vitzthum, V. J. (2013). "Fifty fertile years: anthropologists' studies of reproduction in high altitude natives". Am J Hum Biol. 25 (2): 179–189. doi:10.1002/ajhb.22357. PMID 23382088.
- Simonson, TS; Yang; Huff; Yun; Qin; Witherspoon; Bai; Lorenzo; Xing; Jorde; Prchal; Ge (2010). "Genetic evidence for high-altitude adaptation in Tibet". Science. 329 (5987): 72–75. Bibcode:2010Sci...329...72S. doi:10.1126/science.1189406. PMID 20466884.
- MacInnis MJ, Rupert JL; Rupert (2011). "'ome on the Range: altitude adaptation, positive selection, and Himalayan genomics". High Alt Med Biol. 12 (2): 133–139. doi:10.1089/ham.2010.1090. PMID 21718161.
- Zhang, YB; Li; Zhang; Wang; Yu (2012). "A preliminary study of copy number variation in Tibetans". PLoS ONE. 7 (7): e41768. Bibcode:2012PLoSO...741768Z. doi:10.1371/journal.pone.0041768. PMC . PMID 22844521.
- Bigham, AW; Wilson; Julian; Kiyamu; Vargas; Leon-Velarde; Rivera-Chira; Rodriquez; Browne; Parra; Brutsaert; Moore; Shriver (2013). "Andean and Tibetan patterns of adaptation to high altitude". Am J Hum Biol. 25 (2): 190–197. doi:10.1002/ajhb.22358. PMID 23348729.
- Bigham, A; Bauchet; Pinto; Mao; Akey; Mei; Scherer; Julian; Wilson; López Herráez; Brutsaert; Parra; Moore; Shriver (2010). "Identifying signatures of natural selection in Tibetan and Andean populations using dense genome scan data". PLOS Genetics. 6 (9): e1001116. doi:10.1371/journal.pgen.1001116. PMC . PMID 20838600.
- Alkorta-Aranburu, G; Beall; Witonsky; Gebremedhin; Pritchard; Di Rienzo (2012). "The genetic architecture of adaptations to high altitude in Ethiopia". PLOS Genetics. 8 (12): e1003110. doi:10.1371/journal.pgen.1003110. PMC . PMID 23236293.
- Scheinfeldt, LB; Soi; Thompson; Ranciaro; Woldemeskel; Beggs; Lambert; Jarvis; Abate; Belay; Tishkoff (2012). "Genetic adaptation to high altitude in the Ethiopian highlands". Genome Biol. 13 (1): R1. doi:10.1186/gb-2012-13-1-r1. PMC . PMID 22264333.
- Huerta-Sanchez, E; Jin, X; Asan; Bianba, Z; Peter, B.M; Vinckenbosch, N; Liang, Y (2014). "Altitude adaptation in Tibetans caused by introgression of denisovan-like DNA". Nature. 512 (7513): 194–197. Bibcode:2014Natur.512..194H. doi:10.1038/nature13408. PMC . PMID 25043035.
- McCracken, K. G.; Barger, CP; Bulgarella, M; Johnson, KP; et al. (October 2009). "Parallel evolution in the major haemoglobin genes of eight species of Andean waterfowl". Molecular Evolution. 18 (19): 3992–4005. doi:10.1111/j.1365-294X.2009.04352.x. PMID 19754505.
- "How the Respiratory System of Birds Works". Foster and Smith. Retrieved 21 December 2012.
- Moyes, C.; Schulte, P. (2007). Principles of Animal Physiology, 2/E. Benjamin-Cummings Publishing Company. ISBN 0321501551.
- Grubb, B.R. (October 1983). "Allometric relations of cardiovascular function in birds". American Journal of Physiology. 245 (4): H567–72. PMID 6624925.
- Mathieu-Costello, O. (1990). Histology of flight: tissue and muscle gas exchange. In Hypoxia: The Adaptations. Toronto: B.C. Decker. pp. 13–19.
- Faraci, F.M. (1991). "Adaptations to hypoxia in birds: how to fly high". Annual Review of Physiology. 53: 59–70. doi:10.1146/annurev.ph.53.030191.000423. PMID 2042973.
- Swan, L.W. (1970). "Goose of the Himalayas". Journal of Natural History. 70: 68–75.
- Tibet Environmental Watch (TEW). "Endemism on the Tibetan Plateau". Retrieved 2013-04-16.
- Conservation International. "Tropical Andes: Unique Biodiversity". Archived from the original on 2013-04-23. Retrieved 2013-04-16.
- McCracken KG, Barger CP, Bulgarella M, Johnson KP, Kuhner MK, Moore AV, Peters JL, Trucco J, Valqui TH, Winker K, Wilson RE (2009). "Signatures of High‐Altitude Adaptation in the Major Hemoglobin of Five Species of Andean Dabbling Ducks". The American Naturalist. 174 (5): 610–650. doi:10.1086/606020. JSTOR 606020. PMID 19788356.
- Wilson RE, Peters JL, McCracken KG; Peters; McCracken (2013). "Genetic and phenotypic divergence between low- and high-altitude populations of two recently diverged cinnamon teal subspecies". Evolution. 67 (1): 170–184. doi:10.1111/j.1558-5646.2012.01740.x. PMID 23289570.
- Cai Q, Qian X, Lang Y, Luo Y, Pan S, Hui Y, Gou C, Cai Y, Hao M, Zhao J, Wang S, Wang Z, Zhang X, Liu J, Luo L, Li Y, Wang J, He R, Lei F, Xu J; Qian; Lang; Luo; Xu; Pan; Hui; Gou; Cai; Hao; Zhao; Wang; Wang; Zhang; He; Liu; Luo; Li; Wang (2013). "The genome sequence of the ground tit Pseudopodoces humilis provides insights into its adaptation to high altitude". Genome Biol. 14 (3): R29. doi:10.1186/gb-2013-14-3-r29. PMC . PMID 23537097.
- Facts and Details (of China) (2012). "Tibetan Animals". Retrieved 2013-04-16.
- "High Altitude Plants". Adventurers and Scientists for Conservation.
- Bezruchka, Stephen; Lyons, Alonzo (2011). Trekking Nepal: A Traveler's Guide. The Mountaineers Books. p. 275.
- Elliott-Fisk, D.L. (2000). "The Taiga and Boreal Forest". In Barbour, M.G.; Billings, M.D. North American Terrestrial Vegetation (2nd ed.). Cambridge University Press. ISBN 978-0-521-55986-7.
- National Geographic: Three High-Altitude Peoples, Three Adaptations to Thin Air
- High-Altitude-Hypoxia: Many solutions to one problem
- Adapting to High Altitude
- ScienceDaily: Researchers Solve Questions About Ethiopians' High-Altitude Adaptations
- MIT Technological Reviews: Genetic Adaptations to High Altitude
- How one cinnamon teal becomes two: High altitude adaptation implicated in bird speciation
- Altitude Illness
- Understanding adaptation to high altitude in the Andean region
- BBC: Altitude tolerant
- Physiology of High Altitude Adaptations in Animals
- Understanding Evolution: The mysteries of Tibet
- Scientific resources at the Center for Research on Tibet
- Altitude Research Center: Altitude fast facts
- Living in High Altitudes
- Evolution, Development, and Genomics
- bioquick News: Study Aids Genetic Understanding of High-Altitude Adaptation
- High Altitude: What Happens to the Human Body In the "Death Zone"
- At high altitude, carbs are the fuel of choice
- FAO: The yak in relation to its environment
- Daily Mail: Tibetans 'evolved to cope with living at high altitudes in less than 3,000 years'
- The New Zealand Royal Society: Evolution leap may be fastest ever
- The Yak Genome Database
- Yak Genome Provides New Insights Into High Altitude Adaptation